This invention relates to the field of RF circuits. More particularly, this invention relates to matching networks in RF circuits.
An antenna of a radio frequency (RF) circuit may have varying admittance values, depending on the electrical environment around the antenna. Admittance has a complex numerical value consisting of a real conductance and an imaginary susceptance. For example, an antenna in a cellular phone may have one value of admittance when the cellular phone is held close to a human body and a different admittance value whantenna and another component, such as a transmission line, of the RF circuit coupled to the antenna. The matching network may reduce power losses due to reflected waves caused by an admittance mismatch between the antenna and the component coupled to the antenna. An approach to tuning the matching network so as to reduce admittance mismatch as the antenna admittance varies is disclosed in Provisional Application No. 61/373,273, filed Aug. 12, 2010, the entirety of which is incorporated herein by reference. This application relates to measuring the admittance of an RF frequency component at various instances in time.